An axial flow rotary machine, such as a gas turbine engine for an aircraft, includes a compression section, a combustion section and a turbine section. A flowpath for hot working medium gases extends axially through the engine. The flowpath for hot gases is generally annular in shape.
As the working medium gases are flowed along the flowpath, the gases are compressed in the compression section causing the temperature and pressure of the gases to rise. The hot, pressurized gases are burned with fuel in the combustion section to add energy to the gases. These gases are expanded through the turbine section to produce useful work and thrust.
The engine has a rotor assembly in the turbine section which is adapted by a rotor disk and blades extending outwardly therefrom to receive energy from the hot working medium gases. The rotor assembly extends to the compression section. The rotor assembly has compressor blades extending outwardly across the working medium flowpath. The high energy working medium gases in the turbine section drive the rotor assembly about its axis of rotation. The compressor blades rotate with the rotor assembly and drive the incoming working medium gases rearwardly, compressing the gases and imparting a swirl velocity to the gases.
The combustion section is located between the compression section and the turbine section. The combustion section includes a diffuser plenum and a combustion chamber disposed in the plenum. The diffuser plenum receives the hot, swirling gases from the compression section. The diffuser plenum reduces the velocity of the gases causing the static pressure to rise and distributes the working medium gases to the combustion chamber. The working medium gases entering a conventional aircraft gas turbine engine include air which, because of the presence of oxygen, provides an oxidizer fluid for the combustion chamber. Fuel is mixed with the oxidizer fluid in the combustion chamber and burned to add energy to the gases. The combustion process is not totally efficient causing the production of various emissions which are a function of engine power and the efficiency of the combustion process associated with that power.
At idle power, the combustion efficiency is slightly greater than 99% and is associated with the maximum production of hydrocarbons and carbon monoxide. At higher power, such as take-off, climb and cruise for an aircraft gas turbine engine, the combustion efficiency is greater than 99.9%, and the emissions are very low in hydrocarbons and carbon monoxide. However, the production of oxides of nitrogens and smoke particulates peaks at maximum power. In part, the oxides of nitrogen emissions are associated with operation of the combustion chamber at high temperatures which result from near stoichiometric fuel/air ratios (for efficiency) and the elevated temperature of the air from the compression section. Accordingly, low emission combustion chambers are designed to minimize at low power the production of hydrocarbons and carbon monoxide and to minimize at high power the production of oxides of nitrogen and smoke particulates. And, without having a fuel/air ratio so low at low power that the combustion chamber blows out and does not support combustion (lean blowout).
One example of a combustion chamber designed to reduce such emissions is shown in U.S. Pat. No. 4,045,956 issued to Markowski et al, entitled "Low Emission Combustion Chamber". The combustion chamber shown in Markowski is provided with means that cause hot gases from a pilot burner to swirl about the axis of the combustion chamber. Additional fuel is added to the hot gases and is vaporized as the gases swirl about the axis of the combustion chamber. Thereafter, combustion air is mixed with the fuel rich combustion products to complete the combustion process.
An earlier approach is shown in U.S. Pat. No. 3,872,664 entitled "Swirl Combustor With Vortex Burning And Mixing" issued to Lohmann and Markowski. In this construction, the combustion section includes a main combustion burner and a pilot burner. In one embodiment, the hot combustion products of the pilot burner are mixed with fuel prior to the hot combustion products leaving the pilot zone and entering the main zone of the burner. (The fuel rich combustion products leaving the pilot zone are described as having tangential motion which is essentially dissipated by the time the flow leaves the pilot zone and enters the main zone, col. 2, line 60.) Local columns of air swirling about the axis of swirl tubes 50 enter the main burner and are directed toward, engage and mix with the fuel rich combustion products. Alternatively, fuel may be added through the swirl tubes as shown in FIG. 4.
The above art notwithstanding, scientists and engineers are working under the direction of Applicant's Assignee to develop improved combustion chambers having low emissions.